Double-level residential basement, London NW8

2 May 2017


Basement type: Retrofit Building type: Residential
Type of waterproofing: Type A & C Member: Delta Membrane systems

The Project

This luxurious residential project incorporated a double level basement with the lower level extending out underneath the garden to provide an impressive basement leisure centre with a stunning swimming pool, jacuzzi, and steam room. Knowles & Associates Ltd undertook the following works for the undeground elements of the structure:

  • Excavation and formation of a basement to building footprint and under 7m below garden level.
  • Two/three stage underpinning.
  • Piling. 
  • Mass excavation of spoil.
  • Construction of rear extension.
  • Below slab drainage.
  • Cavity drain membrane Waterproofing.
  • Insulation and screed.
  • Swimming pool shell within lower level basement.  


To waterproof the below ground structure of this project a ‘Type C’ waterproofing system (Delta System 500) was installed internally to manage and control any water ingress. Delta MS500 fixed to the walls and Delta MS20 laid across the floor sealed with the necessary tapes.

Modular drainage was used to drain any water build up to a bespoke Delta packaged pump station situated within the RC concrete slab on the lower level basement.

This collects ground and surface water from the basement walls, floor and from the external light wells. A separate foul pump station was installed to deal with the Foul facilities within the basement.

To waterproof the basement lid of the lower level that extends out underneath the garden Koster Deuxan 2C was applied to the topside of the soffit with a Glass fibre mesh embedded into the first coat to giving it crack bridging qualities.

See Delta Membrane Systems' company profile here.